Do they still run out of steam with the door open? When I first had my vette, the windows would close fine with the door open, but with it shut, they only went up to about a couple of inches from the top. Trouble was, they needed a bit of adjustment as they were rubbing too hard on the seals at the top. I can't lie to you, adjusting them was a complete pain in the a*se!
I've actually had both doors completely apart since then, and removed and cleaned the runners that the window rolls in. This and a bit of adjustment improved the speed a lot, since 20+ years of old grease in the runners doesn't exactly help. The Haynes manual gives quite good details on taking the doors apart, and adjusting the fit afterwards. Just give yourself a day per window, 'cos you're gonna end up swearing at them! It's well rewarding once you've got it all back together again though! Good luck!

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|IMG|http://www.nottingham.ac.uk/~eaztl1/images/vette_4_sig.jpg |/IMG|
Red 1980 350 auto w/ quickshsift
Edelbrock intake / carb
Crane Fireball cam
0 - 60 6.3s